Bathtub enclosure



FIG. 1 is a front/right side perspective view of a bathtub enclosure showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2 thereof; and,

FIG. 4 is a top plan view thereof.

The broken lines are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a bathtub enclosure, as shown and described. 